Maybe it's just because it's early days and your milk supply is just getting established. You might find that when things get going a bit more that the time cuts down.

That's what I would say!

I offer one breast until it is completely empty (you can massage under your armpit too if you feel full there, some women have glands clear back there that need help draining too.)

Then I'd offer the other breast at the next feeding, or offer it if she still wasn't full yet. Sounds like you're doing great mama!